1. Field of Invention
The present invention relates to a boring control method for boring deep holes while minimizing the working time and number of steps of a machine tool.
2. Description of Related Art
Boring control methods found in the prior art include Japanese Patent Application Laid-Open (Kokai) (Kokai) No. H4-240011 “Boring Method.” Here, it is indicated that “in cases where the load torque is equal to or less than a specified torque during boring, the drill feed is continued, and the drill is temporarily withdrawn at the point in time at which the drill has cut in by a specified amount from the position where the drill begins to cut into the workpiece, while in cases where the load torque exceeds a specified torque during boring, the feeding of the drill is stopped, and the drill is temporarily withdrawn. When the drill is withdrawn, the working conditions of boring are altered; boring is re-initiated under the altered working conditions, and boring is ended at the point in time at which the bored hole reaches a specified depth”.
In Japanese Patent Application Laid-Open (Kokai) (Kokai) No. H4-240011 “Boring Method”, which is a boring control method found in the prior art, since “in cases where the load torque is equal to or less than a specified torque during boring, the drill feed is continued, and the drill is temporarily withdrawn at the point in time at which the drill has cut in by a specified amount from the position where the drill begins to cut into the workpiece”, this method has drawbacks. Namely, the number of steps is excessively large, so that the working time is prolonged. Furthermore, if there are numerous step operations, an impact force acts on the drill cutting tip when the drill bites in, so that the drill is easily damaged, and the problem of early wear arises. If the torque limit value which is a threshold value is set at a high value, the drawbacks of extreme wear, damage and impossibility of reutilization are encountered. Moreover, since “the working conditions of boring are altered, and boring is reinitiated under the altered working conditions”, these working conditions cause a stepwise decrease in the feeding rate, so that the problem of a prolonged working time is encountered.